1. Field of the Invention
The invention relates generally to a wheeled vehicle designed to move parked aircraft. In particular, the invention relates to aircraft transport vehicles that move aircraft by lifting the nose landing gear clear of the ground to move the aircraft without the use of connected tow bars.
2. Description of the Prior Art
Aircraft transport tractors commonly employ an attached towbar, attached at a single pivot point, that is used to engage nose gear of aircraft to push or pull the aircraft. The aircraft landing gear remain on the ground at all times during transport by a conventional towbar-type aircraft transport tractor. However, towbarless aircraft transport vehicles, which lift aircraft nose gear up off of the ground, are also in use. Towbarless tractors are designed to eliminate all but the one pivot point to reduce turn limit damage, eliminate jackknifing, and provide increased maneuverability.
FIG. 1 shows a typical towbarless aircraft transport tractor 1 known in the prior art utilizes a scoop or bucket 2 that lays flat on the ground and receives the aircraft landing nose gear wheels. A harness 3 is secured to the aircraft, and the aircraft is pulled into the bucket by a winch located on the tractor. Once the aircraft is winched into the bucket tightly against the bucket wall 4, the bucket is raised and tilted rearward, securing the aircraft and making it possible to tow. As a result of the tilting of the bucket, the geometry of the landing gear may have a forward rake angle, which may place the nose gear in a bind when the aircraft, and hence the nose gear, are turned sharply.
Other lift designs may be used to lift aircraft nose gear for transport. For instance, a scoop or receiver bucket may be placed in front of the aircraft wheels and a set of arms with either powered wheels or free wheeling wheels are placed behind the landing gear wheels. The rearward placed rollers are then pulled forward forcing the aircraft wheels to roll forward into the receiver portion of the device. When the aircraft is secured against the front portion of the receiver, the landing gear wheels are raised and can be transported. Other devices may employ winching devices that winch the aircraft landing gear forward onto a lazy susan turntable. The swiveling turntable allows the tractor to maneuver the aircraft with less steering of the aircraft nose landing gear, and thus less risk of binding the nose gear.
Towbarless aircraft transport tractors of prior art 1 all require that the aircraft be moved from its original position to be captured in the lifting bucket, for example by being winched forward by a harness. Because other equipment may be attached to the aircraft during aircraft servicing, the process of capturing the aircraft into the bucket may need to be deferred until the aircraft is completely free to be moved, thus minimizing the amount of preparation and pre-staging of the transport tractor that may be accomplished and increasing overall transport time. It is therefore desirable to have an aircraft lift mechanism that does not require the aircraft to be moved during the cradling process.
Furthermore, the harness must be manually attached to and released from the aircraft as part of the transport process, which increases transport time and effort. Therefore, it is desirable to have an aircraft lift mechanism that allows an operator to completely cradle and release the aircraft nose gear from the operator's seat of the aircraft transport tractor.
Towbarless aircraft transport tractors 1 of prior art are typically four-wheeled vehicles with fixed drive wheels 45 located at the lifting end of the tractor and steerable wheels 6 located at the opposite end. The fixed wheels 45 are powered and provide tractive force for the tractor 1 and towed aircraft. The weight of the aircraft acts downwardly close to the drive wheels and helps to provide traction.
The two steerable wheels 6 simultaneously pivot within a limited angular range. Because there is a fixed distance between the fixed wheel axle and the steerable wheel axle, a turning radius exists that far exceeds the space actually occupied by the vehicle itself. The longer the distance between axles, the larger the turning radius that is required to change directions of the vehicle. A large turning radius makes maneuvering around tight areas difficult and often dangerous. In an area where movement is constrained, a vehicle with a small turn radius is advantageous. Any increase in maneuvering efficiency and safety generally amounts to significant cost savings. It is desirable, therefore, to have a vehicle with greater maneuverability to enhance the safety of the operator, the aircraft, and the surrounding environment.
Furthermore, towbarless aircraft transport tractors 1 of prior art are single-use specialized vehicles characterized by an integral aircraft lift mechanism. As tractors are used in a number of aircraft servicing operations, such as for towing baggage carts or moving aircraft with conventional towbars, it is advantageous to use a common tractor design that can perform numerous services. Interoperability of tractors reduces capital costs, improves redundancy, and provides operational flexibility. Therefore, it is desirable to incorporate an aircraft lift mechanism in a dolly that can be removably coupled with a multi-purpose tractor.